This invention relates to a method and a device for relative time and position determination for moving objects based on one-way and two-way measurements.
If links between satellites of a constellation are to be used for distance measurement and thus for position determination and clock synchronization, then the measurement results must be transmitted among the satellites of the constellation, if the satellites are supposed to autonomously estimate the orbits and clocks. In a GPS (global positioning system), for example, a signal is sent from one satellite to all the other satellites of the system, and the respective arrival time of the signals is determined in the receiving satellites. These measurement results are digitized in the respective receiving satellites and then sent back as a numerical value to the satellites originally sending the signals.
This procedure has the disadvantage that either relatively high data rates are needed for transmission of the digitized measurement results or there are long intervals of time between two successive orbit or clock determinations.
One object of the present invention is to provide a method and a device for determining the orbits and clocks of satellites which do not have any of the above disadvantages.
This object is achieved by way of a method or a device for relative time and position determinations for moving objects of a constellation in which signals are isochronously transmitted by the objects of the constellation such that each object transmits a unique signal for that object, and signals received by each object of the constellation are transmitted to all other objects of the constellation after a predetermined waiting time, with the waiting time being predetermined individually for each object.
One advantage of the inventive method is that in this way each satellite of the constellation receives a two-way measurement with each satellite of the constellation, to which it is sent back directly, and two combined one-way measurements via another satellite with all the other satellites of the constellation without having to transmit measured values as digital data among the satellites. No measured values need be transmitted because all necessary measured data are generated directly at the receiving satellite from the measurements on the satellite itself and the stipulated nominal sending points in time to the satellites and/or the stipulated waiting times until resending the received signals, which are emitted by each satellite at the start of each measurement period.
With the inventive method, it is thus no longer necessary to transmit digitized measurement data. However, if no more data need be transmitted, it is possible for the transmission to be at a much lower power level and/or to perform measurements with a much better precision at the same power level.